The present invention relates to a process for confining and limiting pollution of an isostatic pressing enclosure in the case of the processing therein of dangerous or radioactive products and when attempts are made, at the end of the pressing operation, to establish whether or not contamination has taken place.
Isostatic pressing is widely used at present for all applications where a product has to be subject to an identical pressure action in all directions. This process can more particularly be used for producing mechanical parts by compaction of a powder, for the compaction of carbon-carbon composite materials, the compaction of tungsten carbide parts, the elimination of defects in certains parts or for compacting radioactive waste before the transportation thereof to a storage location.
The principle of isostatic pressing or compression consists of depositing the material to be processed within an enclosure, into which is introduced a fluid under a high pressure, which can in certain cases be up to 6000 bars. In the case where the operation is performed hot, a furnace is installed within the enclosure and the temperature and pressure are simultaneously raised. The fluids used can be a liquid such as oil, or a neutral gas such as helium or argon or, possibly, nitrogen. The installation generally incorporates a compressor for raising the gas or liquid to the appropriate pressure. The isostatic pressing enclosure is generally shaped like a cylinder, closed at one of its ends by a fast handling plug, the different supply energies of the enclosure entering via a plug located at the other end. As the pressure prevailing in the enclosure is very high, it is necessary to protect it against radial forces which occur. For this purpose, it is possible to reinforce the enclosure wall with a coiled wire and place the same within a "mesh" shaped like a double horseshoe, within which is placed the enclosure, the shape and dimensions of the mesh being such that an accidental expulsion of the plugs is prevented. When the pressing operation is ended, simultaneously with allowing the temperature to return to the ambient temperature, the fluid contained in the enclosure is discharged through a decompression circuit, in order to bring the pressure within the enclosure to a value equal to atmospheric pressure before extracting the processed products.
A special problem arises when the isostatic pressing enclosure is used for the compacting of nuclear waste or, in general terms, toxic or dangerous products. The latter are placed within a flexible material sheath, which is itself enclosed in a container placed within the enclosure. However, during the operation, leaks or a fracture of the container can occur and the gas which has become radioactive can possibly contaminate the different parts of the enclosure, particularly the furnace and the inner walls of the latter. Moreover, the discharge of the gas through the decompression circuit can cause the contamination thereof and the pollution of the atmosphere.
At present, in order to obviate these disadvantages, the users of presses working on polluting, toxic or radioactive products, use a confinement means constituted be a very large glove box, within which is located the enclosure, the compressor or compressors supplying the same, together with the means maintaining the enclosure plug in place during the pressing operation, such as the aforementioned mesh. However, this procedure suffers from the disadvantage that, in the case of contamination, all the members within the glove box are contaminated. It is not always possible to carry out decontamination and all the means risk becoming unusable, which is very costly.